Epicutaneous patch test units are used for skin tests to determine and diagnose causes of allergic contact dermatitis. The patch test units used for liquid or petrolatum based allergens typically include an absorbent pad for absorbing the allergen. Some patch test units include at least one test chamber holding the absorbent pad. The test chambers are arranged on a patch test tape coated with a hypoallergenic adhesive for holding the test chambers on test subject's skin. In other test units, the absorbent pads are arranged directly on the patch test tape without a chamber.
Typically, allergens are loaded in a syringe and carefully injected into the test chambers or directly onto the absorbent pads, in an appropriate quantity. The liquid or petrolatum based allergens are absorbed by the absorbent pad. The patch test unit loaded with the allergens is then applied on the back or other appropriate areas of the test subject's skin, such that the allergens can come in contact with the skin. The test unit is then removed after a predetermined time. The first reading or observation of the test subject's reaction to the allergens takes place immediately after the removal of the test unit and further readings or observations can occur at given intervals of time.
Some patch test units include test chambers that are formed of an aluminum, polyethylene, or polyurethane or other polymer blend. Typically, the test chambers include a reservoir for holding allergens. Some patch test units require a tester to place an absorbent pad in the test chamber at the time of testing. The loose absorbent pad can be easily forgotten. Further, placing of the absorbent pad in the test chamber can often be a tedious and time-consuming process for the tester. As some liquid allergens must be placed in the patch test unit immediately before being applied on the test subject to avoid evaporation of the liquid allergen, such time consuming set up process is undesirable and can negatively impact test results. Further, the loose absorbent pads may become displaced during the patch testing or fall out from the test chamber during preparation, thereby posing a risk of contamination. Other patch test units that include absorbent pads without test chambers also present contamination risks. The patch test units available in the market include, but not limited to, Finn Chambers®, allegEAZE™, Van der Bend Chambers, IQ® and IQ-Ultra® chambers, Curatest® and Curatest® F patch test strips, and Torii patches.
The Finn Chambers® test units, which is available through the assignee of the present application, include aluminum test chambers. To use Finn Chambers® for liquid allergens, the tester must place an absorbent pad in the form of a loose filter paper disc in the aluminum chamber. The loose filter paper disc can present a number of challenges. First, placing the small and thin loose filter paper disc in a small chamber (typically 8 mm or 12 mm in diameter) can be a tedious and time-consuming process. Further, as the filter paper disc is held in place only by a surface tension of the wet filter paper disc holding a liquid allergen, the filter paper disc can easily be displaced or slide out from the center of the chamber, for example, when the test unit is vertically lifted to be applied on the test subject. Sometimes, the filter paper disc may even be displaced from the chamber by test subject's movements during a test period (typically 48 hours.) Further, the aluminum chambers may interact with mercurial compounds or other allergens leading to potential false patch test readings.
The allegEAZE™ patch test systems are also available through the assignee of the present application. The allegEAZE™ patch test systems include injection molded plastic test chambers. This plastic test chamber has a filter paper absorbent pad pressed into the chamber base. Customers of the allegEAZE™ patch test systems have complained that the filter paper absorbent pads often fall out prior to testing. Sometimes, the filter paper absorbent pads are displaced from the test chambers while still in a box and are missing when the patch test system is removed from the box. Because the filter paper absorbent pads are mechanically forced into the test chamber, even if the displaced filter paper absorbent pad is found in the box, it is difficult to correctly place the pad back into the test chamber. If the displaced filter paper absorbent pads are completely missing, the customers either have to discard the whole patch test system, or use them with some test chambers missing the absorbent pad as no extra absorbent pads are provided with the test systems. Such patch test systems are described in Diagnostic Testing Device for the Skin, U.S. Pat. No. 5,325,864, the entire disclosure of which is incorporated herein by reference thereto.
The Van der Bend also has test chambers similar to the allegEAZE™ test chambers, and thus, has the similar missing absorbent pad problems. Dutch Patent No. 8701577 to Van der Bend, the entire disclosure of which is incorporated herein by reference thereto, discloses patch test unit including absorbent pads, which has the similar missing absorbent pad problems.
The IQ-Ultra® patch test units from Chemotechnique MB Diagnostics does not have a true test chamber like the previously described aluminum or plastic test chambers. Rather, IQ-Ultra® patch test unit's reservoir for holding an allergen is provided by a negative space created by a thickness of a square-shaped frame formed of a polymeric foam material, which is arranged on a square-shaped filter element that is secured between a patch test tape and the foam frame. Since the filter element is fixed with adhesives, there is no risk of the filter element being displaced as it was with the previously described test chambers. However, the problem with the IQ-Ultra® is that the square foam frame, which is covered with an adhesive, absorbs the liquid allergen and/or allows the liquid allergen to flow under the foam, thereby contaminating neighboring chambers and/or preventing the allergen from contacting the skin when placed on the test subject. Further, the test chamber is too deep for the allergen absorbed in the filter paper to come in contact with the patient's skin. These test chambers absorb the allergen but do not release sufficiently for accurate testing. Such patch test units are described in Epicutaneous Test Plaster, U.S. Patent Publication No. 2005/0043648, the entire disclosure of which is incorporated herein by reference thereto.
The Curatest® and Curatest® F patch test strips from Lohmann GmbH do not include a true test chamber or a negative space sufficient for a reservoir. These test strips include absorbent pads secured between a patch test tape and a thin plastic ring overlaying the periphery of the absorbent pad. The thin plastic ring is formed of a thin plastic film, thus it provides hardly any negative space. Therefore, the allergen absorbed in the absorbent pad can smear beyond the plastic ring during the test period. Further, the surface area of the absorbent pad exposed to the patient is substantially reduced by the plastic ring to reduce an amount of the allergen that comes in contact with the test subject. Such patch test strips are described in Epicutaneous Test Plaster, U.S. Pat. No. 5,044,372; and Epicutaneous Test Plaster, U.S. Pat. No. 6,142,954; the entire disclosures of which are incorporated herein by reference thereto.
The Torii test patch units have absorbent pads arranged on a patch test tape without a test chamber or a ring cover. There is no negative space reservoir to contain allergens, thus, the allergens can smear beyond the absorbent pads to cause contamination. Further, users of the Torii test patch units including cotton absorbent pads have reported problems with irritations from cotton threads which begin to fray before and/or during testing, thereby resulting in false readings.
There exists, therefore, a need in the art for an improved epicutaneous patch test chamber for liquid or petrolatum-based allergens. The invention disclosed herein provides an improved test chamber and method of making the test chamber. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.